The present invention relates generally to data communication systems and more particularly relates to a system for transporting Ethernet frames over Very high speed Digital Subscriber Line (VDSL) using the HDLC protocol.
There is a growing need among both individuals and enterprises for access to a commonly available, cost effective network that provides speedy, reliable services. There is high demand for a high-speed data network, one with enough bandwidth to enable complex two-way communications. Such an application is possible today if, for example, access is available to a university or a corporation with sufficient finances to build this type of network. But for the average home computer user or small business, access to high speed data networks is expensive or simply impossible. Telephone companies are therefore eager to deliver broadband services to meet this current explosion in demand.
One of the problems is that millions of personal computers have found their place in the home market. Today, PCs can be found in approximately 43% of all United States households and a full 50% of United States teenagers own computers. Virtually every PC sold today is equipped with a modem, enabling communication with the outside world via commercial data networks and the Internet. Currently, people use their PCs to send and receive e-mail, to access online services, to participate in electronic commerce and to browse the Internet. The popularity of the Internet is such that there are an estimated 50 million users around the globe. These figures indicate that in the past few years the personal computer has fueled a dramatic increase in data communications and the corresponding demands on the data networks that carry the traffic.
The Internet serves as a good example of the increased demands that have been placed on data networks. At first, Internet access consisted of text only data transfers. Recently, with the popularity of the World Wide Web (WWW) and the construction of numerous sites with high quality content, coupled with the development of Internet browsers such as Mosaic, Netscape Navigator and Microsoft Explorer, the use of graphics, audio, video and text has surged on the Internet. While graphics, audio and video make for a much more interesting way to view information as opposed to plain text, bandwidth consumption is significantly increased. A simple background picture with accompanying text requires approximately 10 times the bandwidth needed by text alone. Real-time audio and streaming video typically need even more bandwidth. Because of the increased requirement for bandwidth, activities such as browsing home pages or downloading graphics, audio and video files can take a frustratingly long period of time. Considering that the multimedia rich World Wide Web accounts for more than one quarter of all Internet traffic, it is easy to see why the demand for bandwidth has outpaced the supply. In addition, the creative community is pushing the envelope by offering audio and full motion video on numerous sites to differentiate themselves from the millions of other sites competing for maximum user hits.
As use of the Internet and online services continues to spread, so does the use of more complex applications, such as interactive video games, telecommuting, business to business communications and video conferencing. These complex applications place severe strains on data networks because of the intensive bandwidth required to deliver data-rich transmissions. For example, a telecommuter who requires computer aided design (CAD) software to be transported over the data network requires a high-bandwidth data pipeline because of the significant size of CAD files. Similarly, a business to business transaction in which large database files containing thousands of customer records are exchanged also consumes large amounts of bandwidth. The same is true for users seeking entertainment value from sites offering high quality video and audio. The lack of available bandwidth in today""s data networks is the primary barrier preventing many applications from entering mainstream use. Just as processing power limited the effectiveness of early PCs, bandwidth constraints currently limit the capabilities of today""s modem user.
Most computer modem users access data through the standard telephone network, known as plain old telephone service (POTS). Even when equipped with today""s speediest modems, dial up modems on a POTS network can access data only at a rate of 28.8, 33.6 or 56 Kbps. Dial up modem transmission rates have increased significantly over the last few years, but POTS throughput is ultimately limited to 64 Kbps. While this rate may be acceptable for some limited applications like e-mail, it is a serious bottleneck for more complex transactions, such as telecommuting, video conferencing or full-motion video viewing. To illustrate, full motion video compressed, using the Motion Picture Entertainment Group (MPEG)-2 standard requires a data stream of approximately 6 Mbps, or roughly 208 times the throughput of a 28.8 Kbps modem. Thus, using today""s dial up modems, it would take more than 17 days to capture two hours of video. As bandwidth demands continue to grow, providers search for better ways to offer high speed data access. Further complicating the problem is the need to deliver all these complex services at an affordable price.
Today""s most popular data access method is POTS. But as discussed previously, POTS is limited when it comes to large data transfers. An alternative to POTS currently available is Integrated Services Digital Network (ISDN). In the past few years, ISDN has gained momentum as a high-speed option to POTS. ISDN expands data throughput to 64 or 128 Kbps, both from the network to the home and from the home back to the network, and can be technically made available throughout much of the United States and in many other parts of the globe. Similar to POTS, ISDN is a dedicated service, meaning that the user has sole access to the line thus preventing other ISDN users from sharing the same bandwidth. ISDN is considered an affordable alternative, and in general, ISDN is a much better solution for applications such as Web browsing and basic telecommuting. However, like POTS, ISDN is severely limited in applications such as telecommuting with CAD files and full-motion video viewing. The latter requires roughly 39 times the throughput than that provided by ISDN.
Multichannel multipoint distribution service (MMDS), a terrestrial microwave wireless delivery system, and direct broadcast satellite (DBS), such as DirecTv and US Satellite Broadcasting (USSB), are wireless networks. They both deliver high bandwidth data steams to the home, referred to as downstream data, but neither has a return channel through which data is sent back over the network, referred to as upstream data. Although it is a relatively affordable system to deploy for broadcast applications, because it requires no cable wires to be laid, it falls short in interactive access. In order to use a wireless system for something as basic as e-mail, an alternate technology such as a telephone line must be used for the upstream communications.
Another available network delivery system is asymmetric digital subscriber line (ADSL). Offering a downstream capacity of 6 Mbps or more to the home, ADSL has the downstream capacity to handle the most complex data transfers, such as full motion video, as well as an upstream capacity of at least 500 Kbps. However, due to its limitation of upstream bandwidth capacity, it essentially is a single service platform. Also, since it has to overcome the challenge of reusing several thousand feet of existing twisted pair wiring, the electronics required at each end of the cable are complex, and therefore currently very expensive. the challenge of reusing several thousand feet of twisted pair wiring, the electronics required at each end of the cable are complex, and therefore currently very expensive.
Hybrid fiber coax (HFC), a network solution offered by telephone and cable companies, is yet another option for delivering high bandwidth to consumers that is known in the art. However, HFC has limitations. HFC networks provide a downstream capacity of approximately 30 Mbps, which can be shared by up to 500 users. Upstream bandwidth is approximately 5 Mbps and also is shared. A disadvantage with HFC is that shared bandwidth and limited upstream capacity become serious-bottlenecks when hundreds of users are sending and receiving data on the network, with service increasingly impaired as each user tries to access the network.
It is a current trend among telephone companies around the world to include existing twisted pair copper loops in their next generation broadband access networks. Hybrid Fiber Coax (HFC), a shared access medium well suited to analog and digital broadcast, comes up short when utilized to carry voice telephony, interactive video and high speed data communications at the same time.
Fiber to the home (FTTH) is still prohibitively expensive in the marketplace that is soon to be driven by competition rather than costs. An alternative is a combination of fiber cables feeding neighborhood Optical Network Units (ONUs) and last leg premises connections by existing or new copper. This topology, which can be called fiber to the neighborhood (FTTN), encompasses fiber to the curb (FTTC) with short drops and fiber to the basement (FTTB), serving tall buildings with vertical drops.
One of the enabling technologies for FTTN is very high rate digital subscriber line (VDSL). VDSL is an emerging standard that is currently undergoing discussion in ANSI and ETSI committees. The system transmits high-speed data over short reaches of twisted pair copper telephone lines, with a range of speeds depending upon actual line length.
The VDSL standard as provided by the VDSL Draft Specification being drafted by the ANSI TIE1.4 Technical Subcommittee, provides guidelines for the transmitter and receiver within the VDSL modem. The connection between the VDSL modem and the Customer Premises Equipment (CPE) specifies a number of signals including TxData, RxData, RxErr, TxCLK, RxCLK and TxSOC and RxSOC. The latter two signals, i.e., TxSOC and RxSOC, provide an indication of the start of the payload within the respective VDSL frame to the CPE for both transmission and reception.
It is intended that the SOC signal be used by the CPE to synchronize the transmission and reception of the data to and from VDSL modem. In the case of transporting Ethernet data over the VDSL facility, a problem arises, however, when attempting to sync Ethernet frames to VDSL frames. The problem with using these SOC signals is that the VDSL frame is a fixed number of bytes, e.g., 256 bytes, whereas the Ethernet frame may vary from 64 to 1518 bytes. Designing and implementing the circuitry, e.g., state machines, timing and framing circuits, etc., to perform the protocol matching, i.e., sync timing between Ethernet frames and VDSL frames is very complicated and hence expensive to implement.
It is desirable to have a means of transporting Ethernet frame data over a VDSL transport facility that does not require the complicated circuitry and state machines when utilizing the SOC signals provided by the VDSL modem.
One of the challenges in implementing a mechanism of transporting Ethernet traffic over VDSL is the requirement of enabling the recipient to synchronize to the Ethernet stream, i.e., to enable the receiver to xe2x80x98knowxe2x80x99 where the Ethernet frame starts and where it ends. The Ethernet frames are normally conveyed to the Ethernet transceiver from the line utilizing Manchester encoding. This code comprises three states which are IDLE where the signal is constantly high, a xe2x80x981xe2x80x99 or a xe2x80x980xe2x80x99 bit wherein each contains a transition at the midpoint of the bit period.
The direction of the transition determines whether the bit is interpreted as a xe2x80x980xe2x80x99 or a xe2x80x981xe2x80x99. The first half is the actual value and the second half is the complement of the actual bit value. By using this coding scheme, the transceiver is able to xe2x80x98knowxe2x80x99 where an Ethernet packet starts and where it ends.
This coding scheme, however, cannot be applied to a VDSL transport system because the VDSL receiver would receive at its input either a xe2x80x981xe2x80x99 or a xe2x80x980xe2x80x99 without any mechanism for the user to indicate to the VDSL transceiver where an incoming Ethernet frame starts or where it ends, e.g., TxEnable or RxEnable. The same problem is present in the reverse direction as well, wherein the VDSL transceiver transmits a bit stream with no mechanism to indicate where in the bit stream the Ethernet frame starts or ends.
As described above, a typical VDSL transceiver provides a SOC signal for the transmit and receive directions. It is intended that these signals permit the user to synchronize the Ethernet frames. Because these frames are of variable length, however, achieving synchronization using the SOC signals is relatively complicated to implement and requires a large amount of additional logic. Thus it would be desirable to have an alternative means of synchronizing the Ethernet frame data at the receiver.
The present invention is an apparatus for and method of encapsulating Ethernet frame data in Very high speed Digital Subscriber Line (VDSL) frames. The VDSL frames are transmitted over a point to point VDSL link where they are subsequently extracted and forwarded as standard Ethernet frames. The invention utilizes the widely known HDLC communications protocol to encapsulate Ethernet frames for transmission over the VDSL transport facility of the invention. An HDLC controller is employed to perform the conversion between Ethernet frames and HDLC frames.
A typical VDSL facility transport system comprises an Ethernet to VDSL Consumer Premises Equipment (CPE) coupled to a DSL Access Multiplexor (DSLAM) over a VDSL transport facility. The DSLAM is typically located at the curb or before the xe2x80x98last milexe2x80x99 in a subscriber loop. The Ethernet to VDSL CPE functions to receive a 10BaseT Ethernet signal and encapsulate the Ethernet frame into an HDLC frame for transmission over the VDSL facility utilizing the HDLC protocol. Likewise, the Ethernet to VDSL CPE also functions to receive a VDSL signal in HDLC protocol format, extract Ethernet frames therefrom and output them as standard 10BaseT Ethernet signals.
The DSLAM is adapted to receive HDLC protocol formatted frames, extract Ethernet frames therefrom and generate and output a standard Ethernet signal. Likewise, the DSLAM is also adapted to receive standard Ethernet frames from an Ethernet input signal and encapsulate them in HDLC frames for transmission over the VDSL facility.
In accordance with the invention, the SOC signals provided by the VDSL transceiver are not utilized in transmitting the Ethernet frame data over the VDSL facility. Ethernet frames are encapsulated within HDLC frames and transmitted on the wire pair without regard to the state of the SOC signals. This overcomes the problems associated with synchronizing the transmission of the Ethernet data with the SOC signals.
The characteristics of the HDLC controller, i.e., the sync flag, are used in the present invention to provide the receiving station with an indication of the start of a HDLC frame. The bit stuffing capabilities built into the HDLC controller prevent the occurrence of a sync flag in the data stream.
The receiving station performs standard HDLC reception to determine whether the preamble detected is a sync flag indicating the start of a HDLC frame. The payload of the VDSL frame carries Ethernet frame data that can range from 60 to 1514 bytes. Note that before HDLC encapsulation, the 4 byte Ethernet CRC is extracted.
An Ethernet controller is used to receive and transmit Ethernet frames to and from the Ethernet physical layer transceiver. Both the HDLC controller and the Ethernet controller can be implemented utilizing a commercially available microprocessor or microcontroller.
There is provided in accordance with the present invention a method of transporting Ethernet frames over a Very high speed Digital Subscriber Line (VDSL) transport facility coupling a first communication device and a second communication device, the method comprising the steps of receiving an input Ethernet frame data on the first communication device from a first Ethernet compatible communication device coupled thereto, encapsulating the received Ethernet frame within a High level Data Link Control (HDLC) frame, transmitting the HDLC frame over the VDSL transport facility, receiving HDLC frame data on the second communication device, extracting the Ethernet frame from the received HDLC frame and generating an output Ethernet frame therefrom and transmitting the output Ethernet frame to a second Ethernet compatible communication device coupled to the second communication device.
The step of encapsulating comprises the step of stripping off the preamble, start of frame fields and Cyclic Redundancy Check (CRC) fields from the Ethernet frame and calculating a new CRC before placing the Ethernet frame in the HDLC frame. The step of generating comprises the step of adding Ethernet preamble and Ethernet start of frame fields and calculating a new CRC and appending it to the extracted Ethernet frame.
There is also provided in accordance with the present invention an Ethernet transport system for transporting Ethernet frames over one or more Very high speed Digital Subscriber Line (VDSL) transport facilities, the system comprising a plurality of channels wherein each channel comprises an Ethernet to VDSL Customer Premise Equipment (CPE) adapted to encapsulate Ethernet frames from a first Ethernet source into HDLC frames for transmission over the VDSL transport facility and to extract Ethernet frames from HDLC frames received over the VDSL transport facility, an access multiplexor adapted to interface with the plurality of channels, the access multiplexor adapted to encapsulate Ethernet frames from a second Ethernet source into HDLC frames for transmission to one of the plurality of channels and to extract Ethernet frames from HDLC frames received over the plurality of channels.
Each channel in the system comprises a microcontroller adapted to function as both an Ethernet controller and an HDLC controller.
There is further provided in accordance with the present invention an Ethernet transport system for transporting Ethernet frames over one or more Very high speed Digital Subscriber Line (VDSL) transport facilities, the system comprising a plurality of channels wherein each channel comprises an Ethernet to VDSL Customer Premise Equipment (CPE), each CPE comprising means for receiving an Ethernet frame from a first Ethernet source and encapsulating it within a High level Data Link Control (HDLC) frame, means for transmitting the HDLC frame onto one of the VDSL transport facilities, means for receiving the HDLC frame from one of the VDSL transport facilities and means for extracting the Ethernet frame from the HDLC frame and forwarding it to the first Ethernet source, an access multiplexor adapted to interface with the plurality of channels, the access multiplexor comprising an Ethernet switch having a plurality of ports, means for receiving from each channel, HDLC frames from a corresponding VDSL transport facility, means for extracting Ethernet frames from the HDLC frames and inputting then to a port on the switch, means for transmitting Ethernet frames from the Ethernet switch to a second Ethernet source, means for receiving Ethernet frames from the second Ethernet source and inputting them to the switch, means for encapsulating the Ethernet frames output of the switch into HDLC frames and means for transmitting the HDLC frames onto one of the VDSL transport facilities
The means for encapsulating and extracting on each of the channels comprises a microcontroller adapted to function as an Ethernet controller and an HDLC controller.